What
do you say when a kid asks you: “Which
came first, the chicken or the egg?”

by Christopher Michael Langan

Some people
believe that children should be allowed to use their minds
as freely and imaginatively as possible, without attention
to the tedious laws of rationality.Others think that a child is never too young to get
his or her first dose of logical and scientific reasoning.But in any case, a child with the intellectual
maturity to ask a question like “which came first, the
chicken or the egg?” is probably ready for a valuable
lesson in logic and biology…more of a lesson, perhaps,
than many of us are ready to give.This little essay aims to change all that, and
thereby protect you and your pint-size inquisitors from the
perils of ignorance (and specifically, being recognized as
an incurable case thereof!).

The
question “which came first, the chicken or the egg?”
looks at first glance like a matter of straightforward
reproductive biology.But
before we can even begin to answer this question, we must
define our terms.So
actually, it is a classic case of semantic ambiguity…a
problem of meaning and interpretation.Specifically, while the term “chicken” is
biologically unambiguous – we all know what a chicken
looks, sounds and tastes like - the term “egg” is
somewhat more general and is therefore a possible source of
ambiguity.Do
we mean (1) just any egg, or (2) a chicken egg?And if we’re talking about a chicken egg, then is a
“chicken egg” (2a) an egg laid by a chicken, (2b) an egg
containing a chicken, or (2c) both?Reformulating the question to reflect each possible
meaning of “egg” leads to four distinct versions of the
chicken-or-egg question.

1.Which came first, the chicken or (just any old) egg?

2a.Which came first, the chicken or an egg laid by
a chicken?

2b.Which came first, the chicken or an egg containing
a chicken?

2c.Which came first: the chicken, or an egg laid by and
containing a chicken?

Contrary to
popular belief, there is indeed a definite answer to each of
these questions.Specifically,
the answers are:(1)The egg.(2a)The chicken.(2b)The egg.(2c)The chicken.Given
some knowledge of logic and biology, these answers are not
hard to verify.To
get this show on - or should that be across? - the road,
let’s go through them in order.

First,
consider question 1: which came first, the chicken or (just
any old) egg?This
question is answered “the egg” because species that lay
eggs have been around a lot longer than modern chickens.For example, we have plenty of fossil evidence that
dinosaurs laid eggs from which baby dinosaurs hatched, and
dinosaurs predate chickens by millions of years.Indeed, a growing body of research indicates that
dinosaurs were among the biological ancestors of
chickens!

Now let’s
look at question 2a: which came first, the chicken or an egg
laid by a chicken?The answer to this question is “the chicken” on
semantic grounds alone.That is, if a chicken egg must be laid by a chicken,
then before a chicken egg can exist, there must by
definition be a chicken around to lay it.And question 2c - which came first, the chicken or an
egg laid by and containing a chicken? - is answered
the same way on the same grounds; logically, the fact that a
chicken egg must be laid by a chicken precedes and therefore
“dominates” the (biologically subsequent) requirement
that it contain a chicken.So whereas we needed paleozoological evidence to
answer question 1, questions 2a and 2c require practically
no biological knowledge at all!

Having
saved the best for last, let us finally consider the most
interesting version, 2b:which came first, the chicken or an egg containing
a chicken?This
version is interesting because an egg containing a chicken
might have been laid by a chicken or a non-chicken,
which of course affects the answer.Thanks to modern genetic science, we can now be sure
that the egg came first.This is because reproductive mutations separating a
new species from its progenitor generally occur in
reproductive rather than somatic DNA and are thus expressed
in differences between successive generations, but not in
the parent organisms themselves.While the somatic (body) cells of the parents
– e.g. wing cells, drumstick cells and wishbone cells -
usually contain only the DNA with which they were conceived,
germ (reproductive) cells like ova and spermatozoa
contain non-somatic DNA that may have been changed before or
during mating by accidental deletion, insertion,
substitution, duplication or translocation of nucleotide
sequences.This
is what causes the mutation that results in the new species.

Where an
animal qualifies as a member of a given species only if its
somatic DNA (as opposed to its reproductive DNA) conforms to
the genotype of the species, the parents of the first member
of a new species are not members of that new species.At the same time, all the biological evidence says
that the ancestors of modern chickens were already oviparous
or egg-laying…that a male and a female member of the
ancestral species of the modern chicken, call this species
“protochicken”, mated with each other and created an
egg.(Could the
first chicken have evolved from a viviparous or live-bearing
species, and after being born alive, have started laying
eggs?All the
biological evidence says “no”.)But because their act of mating involved a shuffling
of reproductive genes that were not expressed in the body of
either parent – if they had been expressed there,
the parents would themselves have been members of the new
species - the fetus inside the egg was not like them.Instead, it was a mutant…a modern chicken!

Only two
loose ends remain: the “gradual” and “sudden”
extremes of the evolutionary spectrum.These extremes are evolutionary gradualism -
Darwin’s original slow-paced timetable for natural
selection - and punctuated evolution, as advocated
more recently by evolutionary theorists including the
controversial Stephen J. Gould.

Gradualism
says that mutations are biologically random, but subject to
a selection process determined by environmental (external)
conditions to which species must adapt over the
course of many generations.Taken to the limit, it implies either that each minor
mutation that occurs during the evolutionary change of one
species into another is random and independent of any other
mutation, in which case a useful combination of mutations is
highly improbable, or that each individual mutation confers
a selective advantage on the mutant…that every
evolutionary advantage of a new species over its precursor
decomposes into smaller advantages combined in a more or
less linear way.Unfortunately,
this makes it almost impossible to explain complex
biological structures that do not break down into smaller
structures useful in their own right…structures like
bacterial cilia and flagella, and even the human eye.

The
hypothetical gradualistic evolution of one species into
another via mutations accumulated over many generations
leads to the following question: when does the quality and
quantity of mutations justify a distinction between
“species”…when does a protochicken become a chicken?It’s a good question, but our chicken-or-egg
answers remain valid no matter how we answer it.

At the
other extreme, evolution sometimes appears to progress by
leaps and bounds, moving directly from the old to the new in
“punctuated” fashion.And to complicate matters, this sometimes seems to
happen across the board, affecting many species at once.The most oft-cited example of punctuated evolution is
the Cambrian Explosion.Whereas sedimentary rocks that formed more than about
600 million years ago are poor in fossils of multicellular
organisms, slightly younger rocks contain a profusion of
such fossils conforming to many different structural
templates.The
duration of the so-called “explosion”, a mere geological
eyeblink of no more than 10 million years or so, is
inconsistent with gradualism; new organs and appendages must
have been popping out faster than the environment alone
could have selected them from a field of random mutations.Clearly, the sudden appearance of a new appendage
would leave little doubt about the evolutionary demarcation
of ancestral and descendant species.

But the
kind of punctuated evolution that occurs between generations
is not the end of the line in sheer biological acceleration.Sometimes, an evolutionary change seems to occur
within the lifespan of a single organism!For example, in the spirit of “ontogeny
recapitulates phylogeny”, insect metamorphosis almost
seems to hint at an evolutionary process in which an ancient
grub or caterpillar underwent a sudden transformation to
something with wings and an exoskeleton…or alternatively,
in which a hard-shelled flying bug suddenly gave birth to an
egg containing a soft and wormy larva.While that’s not what really happened – as is so
often the case, the truth lies somewhere in the middle -
what occurred was just as marvelous and just as punctuated.

What seems
to have happened was this.Due to a reproductive mutation, a whole sequence of
evolutionary changes originally expressed in the fetal
development of an ancestral arthropod, and originally
recapitulated within the womb and egg it inhabited, were
suddenly exposed to the environment, or at least to the
hive, in a case of “ovum interruptus”.A fetal stage of morphogenesis that formerly occurred
within womb and egg was interrupted when the egg hatched
“prematurely”, making the soft fetus into an equally
soft larva and giving it a valuable opportunity to seek
crucial nourishment from external sources before being
enclosed in a pupa, a second egg-like casing from
which it later hatched again in its final exoskeletal form.So metamorphosis turns out to be a case of biological
common sense, providing the fetus-cum-larva with an
opportunity to acquire the nourishment required for the
energy-consuming leap into adulthood.

Does this
affect our answer to the chicken-or-egg question?Not really.For
even where the life cycle of an organism includes distinct
morphological stages, the DNA of egg-laying insects does not
change after conception.And since it is reproductive and not somatic DNA
modification that distinguishes one species from the next in
line, our answers stand firm.(Of course, this says nothing of science fiction
movies in which something bizarre and insidious causes
runaway mutations in the somatic DNA of hapless humans,
causing them to evolve into monsters before our very eyes!Such humans have either undergone a random or
radiation-induced “meta-mutation” whereby their genetic
code suddenly rearranged itself to incorporate a
self-modification routine that is executed somatically,
within their own cells, or they are the victims of a space
virus which inserted such a routine into their DNA for its
own nefarious purposes.)

OK…perhaps
there’s yet another loose end.Asking which of two things came first implies that
time flows in a straight line from past to future (those are
the “loose ends”).But what if time were to flow in either direction, or
even to loop around, flowing in what amounts to a circle?No more loose ends.In fact, loops have no ends at all!But in this case, the answer depends on whether
we’re on the forward or reverse side of the loop, heading
towards the future or the past.Another way to formulate this question: does the
cause lead to the effect, or is there a sense in which the
effect leads to the cause?Suffice it to say that no matter which way we choose
to go, the original answers to the four versions (1, 2a, 2b
and 2c) of the chicken-or-egg question are all affected the
same way.They
are either all unchanged or all reversed, with no additional
ambiguity save that pertaining to the direction of time (not
a problem for most non-physicists and non-cosmologists).

Now that
we’ve tied up every last loose end, what about the most
important question of all, namely what to tell a curious
child?The
answer: take your pick of versions.Some kids will prefer the dinosaur angle of version
1; some kids will prefer the “birds and bees”
reproductive biology lesson of version 2b.In my opinion, if we limit ourselves to one version
only, the most valuable explanation is probably that of 2b;
but due to its relative complexity, a younger child can
probably derive greater benefit from a T.
Rex-versus-Triceratops embellishment of version 1.To exhaust the golden opportunities for logical and
scientific instruction, one should of course answer all four
versions.But
no matter which way you go, make sure the child knows
exactly which version(s) of the question you’re answering.If you leave out the one he or she had in mind,
you’ll no doubt be egged on until it gets answered!